蒟蒻求助！！不知道哪里有问题！帮忙看下吧

#include <bits/stdc++.h>
using namespace std;
int n;
char mp[20][20];
char ans[20][20];
bool vis1[20][20];
bool vis2[20][20];
int ty[4] = {1,0,-1, 0};
int tx[4] = {0,1,0,-1};
queue <int> qx;
queue <int> qy;
queue <int> mx;
queue <int> my;
int bfs(int x,int y)
{
    mx.push(0);
    my.push(0);
    qx.push(x);
    qy.push(y);
    while(!qx.empty() && !qy.empty() && !mx.empty() && !my.empty())
    {
        if(mp[qx.front()][qy.front()] != ans[mx.front()][my.front()])
        {
            while(!qx.empty() && !qy.empty())
            {
                qx.pop();
                qy.pop();
            }
            while(!mx.empty() && !my.empty())
            {
                mx.pop();
                my.pop();
            }
            
            return 0;
        }
        for(int i = 0; i<4; i++)
        {
            int dx = qx.front()+tx[i];
            int dy = qy.front()+ty[i];
            int nx = mx.front()+tx[i];
            int ny = my.front()+ty[i];
            if(dx >= 0 && dy >= 0 && dx < n && dy < n && vis1[dx][dy] == 0)
            {
                qx.push(dx);
                qy.push(dy);
                vis1[dx][dy] = 1;
            }
            if(nx >= 0 && ny >= 0 && nx < n && ny < n && vis2[nx][ny] == 0)
            {
                mx.push(nx);
                my.push(ny);
                vis2[nx][ny] = 1;
            }
        }
        qx.pop();
        qy.pop();
        mx.pop();
        my.pop();
    }
    return 1;
}
int fanzhuan()
{
    for(int i = 0; i < n; i++)
    {
        for(int j = 0; j<n/2; j++)
        {
            swap(mp[i][j],mp[i][n-1-j]);
        }
    }
    return 0;
}
int main()
{
    int n;
    cin >> n;
    for(int i = 0; i<n; i++)
    {
        for(int j = 0; j<n; j++)
        {
            cin >> mp[i][j];
        }
    }
    if(bfs(0,n-1))
    {
        cout << 1;
        return 0;
    }
    memset(vis1,0,sizeof vis1);
    memset(vis2,0,sizeof vis2);
    if(bfs(n-1,n-1))
    {
        cout << 2;
        return 0;
    }
    memset(vis1,0,sizeof vis1);
    memset(vis2,0,sizeof vis2);
    if(bfs(n-1,0))
    {
        cout << 3;
        return 0;
    }
    memset(vis1,0,sizeof vis1);
    memset(vis2,0,sizeof vis2);
    fanzhuan();
    if(bfs(0,0))
    {
        cout << 4;
    }
    memset(vis1,0,sizeof vis1);
    memset(vis2,0,sizeof vis2);
    if(bfs(0,n-1) || bfs(n-1,n-1) || bfs(n-1,0))
    {
        cout << 5;
        return 0;
    }
    memset(vis1,0,sizeof vis1);
    memset(vis2,0,sizeof vis2);
    fanzhuan();
    if(bfs(0,0))
    {
        cout << 6;
        return 0;
    }
    cout << 7;
    return 0;
}